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Frankfurt auto show: Mercedes-Benz F125 previews next S-class

September 11, 2011

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At the Frankfurt motor show,Mercedes-Benz revealed its vision of how the range-topping S-class coupe will evolve against a backdrop of increasingly tightening emission standards with the unveiling of a bold new research vehicle called the F125.

Billed as rolling laboratory for the sort of driveline technology Mercedes expects to include on its luxury cars in the not-too-distant future, the big hydrogen-powered car gets an advanced fuel cell that, in theory, is capable of providing it with the performance to beat even the most powerful of today's S-class coupe models, the S600, while endowing it with zero-emission performance.

The latest in a long line of research cars, the F125 was conceived as a styling indicator for the next generation of Mercedes models. It advances the design lineage evident on the last of Mercedes-Benz's research cars, the F800 Style, with bolder detailing aimed at giving it the sort of presence expected of a car at the upper end of the luxury spectrum.

Despite its research-car billing (the F in the name derives from the German word forschung, or research), high-ranking officials have confirmed to Autoweek that certain elements of the F125's exterior design--including its grille and side feature line treatment--will be mirrored on the new S-class, set to debut in 2013, and the successor to today's CL, which is expected to launch in 2014, first as a coupe then, for the first time, as a convertible.

The F125 also reveals the ideas that Mercedes is pursuing for future interior design. Together with an uncharacteristic (by S-class standards) wraparound dashboard and prominent center console, the big four-seater also has an advanced, new command system showcasing the contemporary interfaces and graphics we can expect to see on future Mercedes models.

It's based around a carbon-fiber-reinforced plastic sandwich-platform structure designed specifically to house an integral hydrogen tank. Clothed in a body that combines carbon-fiber-reinforced plastic, aluminum and steel, the concept does without conventional B-pillars and uses a new interpretation on the company's signature gullwing doors.

Continuing the futuristic theme, the F125 gets a state-of-the-art fuel-cell system that uses hydrogen to create electricity, which in turn powers a series of electric motors. A development of the system used in the B-class F-Cell, this brings together ideas the German carmaker is studying in a bid to bring hydrogen into the motoring mainstream.

"With the F125, we want to show that large, comfortable and safe coupes with traditional Mercedes-Benz strengths have a future, partly because they are able to operate with no emissions," says Thomas Weber, head of research and development.

At the heart of the new system is a specially designed hydrogen tank that is integrated into the floor assembly of the F125. Unlike the cylindrical tanks in use today that can withstand pressure of up to 10,000 psi, the new tank design acts a structural element. It draws on technology that Mercedes describes as being in the early stages of research. The structural tank can be filled at a pressure of just 435 psi.

"The structural hydrogen tank represents a technological revolution and opens up completely new perspectives with respect to architecture and range," says Weber. "In the future, it will be possible to integrate the hydrogen tanks into the structure and achieve ranges equal or better to those of current diesel models with no loss of interior space."

Hydrogen from the tank is converted by a fuel-cell stack into electricity, which in turn is stored in a 10-kilowatt-hour lithium-sulfur battery mounted behind the rear seats. A plug-in feature also recharges the F125's battery.

The electricity powers four brushless electric motors, which in a layout similar to that of the upcoming SLS E-cell are mounted low at each corner to provide the F125 with full time four-wheel drive. The motors at the front each deliver 68 hp and 55 lb-ft, with those at the rear rated at 136 hp and 147 lb-ft each. The continuous output is put at 231 hp, with a maximum of 313 hp available for short bursts of full-force acceleration.

Mercedes-Benz's computer simulations suggest the high-tech F125 would be capable of providing 0-to-62-mph acceleration in 4.2 seconds--better than today's V12 S600, which makes the sprint in a claimed 4.6 seconds. The massive torque load sent to all four wheels also provides for theoretical 50-to-75-mph rolling acceleration of just 3.2 seconds. The target top speed, meanwhile, would be limited to 137 mph to preserve the battery charge.

As impressive as the performance figures are, they pale next to the F125's consumption claims. Mercedes-Benz puts hydrogen consumption at just 0.79 kilogram per 62 miles--a figure equivalent to 87 mpg. Tailpipe emissions amount to nothing but some water vapor.